How do MEP plans coordinate with the structural drawings on an ADU?

Pipes, ducts and wires have to pass through or around the framing without weakening it, and equipment has to sit where the structure can support it. Building codes limit how much studs, joists and rafters can be notched or bored, and shear walls have their own penetration limits. Coordinating MEP routing with the structural plans before submittal helps avoid field cuts that fail inspection.

Framing limits that drive MEP routing

The Los Angeles Department of Building and Safety's bulletin on cutting, notching and boring wood framing summarizes limits that apply unless a licensed engineer or architect provides an alternate design:

• Studs. In exterior walls and bearing partitions, notches may not exceed 25 percent of the stud width; nonbearing partitions allow 40 percent. Bored holes may be up to 40 percent of the stud width, or up to 60 percent in nonbearing walls or doubled studs, and must stay at least 5/8 inch from the edge.
• Joists and rafters. End notches up to one-fourth of the depth; notches in the top or bottom up to one-sixth of the depth and not in the middle third of the span; bored holes no larger than one-third of the depth and not within 2 inches of the top or bottom.
• Shear walls. Openings in a shear wall panel may total no more than 20 percent of the wall length, with each opening no more than 4 1/2 inches in any direction. Penetrations of top and sill plates in shear walls have separate limits.
• Walls between units. Where a wall or floor separates two dwelling units, the bulletin calls for 3 inches of clearance around piping for sound control.

The bulletin ties these limits to the residential code sections on joists, studs and rafters (R502.8, R602.6 and R802.7.1). Local amendments can differ.

Coordination points to check

• Wet walls. Drain stacks and fittings need cavity depth, and horizontal runs through studs are capped by the bore limits. Plan bathroom and kitchen walls with the framing, not after it.
• Duct and line-set routes. Confirm ducts, refrigerant lines and condensate drains have a path through the floor or roof framing. Engineered members such as trusses and manufactured joists have their own rules for holes, so ask the structural designer before routing through them.
• Equipment support. Wall-mounted condensers, water heaters and panels need backing or support shown somewhere in the set.
• Shear walls and hold-downs. Check with the structural designer before placing a panel, a large duct or a drain stack in a shear wall segment.
• Slab work. Under-slab drains in a new slab or garage conversion must line up with the foundation plan and any new footings.

When to bring in the structural designer

If a pipe or duct cannot fit within the limits, the fix is a framing change or an engineered detail, not a field cut. Settle those before submittal so the structural and MEP sheets agree.

What this means for your MEP plans

MEP Plans USA draws its sheets over your architectural plans; sharing the structural sheets as well, when you have them, helps catch conflicts before plan check. Field changes that alter approved routing may need a revision. See how MEP plans relate to architectural plans and the complete ADU MEP guide. Framing rules vary with local amendments, so confirm with your building department and structural designer.

Sources: dbs.lacity.gov.